It is narrated from Sayyiduna Ali (may Allah be pleased with him): The obligatory prostrations in the Qur'an are four: in Surah al-Sajdah, Ha-Mim al-Sajdah, Surah al-Najm and Surah al-Alaq.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3714
Hadith Gradingمحدثین:حسن
Hadith Takhrij«حسن۔ اخرجه الحاكم في المستدرك 3957»